1. Field of the Invention
The present invention relates generally to warning light devices, and more particularly to a device for producing integrated directional light from a plurality of LED light sources.
2. Description of the Related Art
Lights designed to serve illumination, warning or signaling functions must produce light of different intensity, duration and pattern. Within any broad category, such as warning lights, lights designed for a particular application, for example aircraft warning lights, may require a very different intensity and light pattern than a warning light designed for an emergency vehicle such as a police car or fire truck.
The prior art contains numerous examples of alternative light sources, reflectors and lenses arranged to produce particular intensities and distributions of light suited for a particular purpose. Of primary concern to designers of lights are efficiency and accuracy. Efficiency relates to producing the maximum amount of light per unit of applied energy. Accuracy relates to directing that light into the desired pattern with minimal losses. Losses are incurred each time light is reflected or passes through a lens. Light that is not directed to reinforce the desired pattern is effectively lost.
Until recently, light-emitting diodes (LEDs) were extremely limited in the quantity and quality (candela vs. viewing angle) of light produced, rendering them unsuitable for many warning and illumination applications. The viewing angle is the angle, measured with respect to the axis through the center of the lens of the LED, where the light intensity has fallen to fifty (50%) of the on-axis intensity.
Recent advances in LED technology have resulted in LEDs having significantly improved light output both in terms of quantity and quality. High-output, or “high flux” LEDs now produce between 18 and 55 lumens each, making them a practical light source for use in signaling and warning illumination. High-output LEDs have significantly greater luminous flux than previous LEDs, however, the total luminous flux from each LED (15–40 lumens) is still relatively small when compared to light sources such as a halogen bulb. Thus, it is typically necessary to concentrate the light output of multiple LEDs in a compact array to produce a light source with the required luminous intensity and radiation pattern.
The light radiation pattern from an LED depends on the shape of the lens molded around the die of the LED. The most common lens shapes are high dome “lambertian”, low dome “batwing” and side emitting. Each of these lenses produces a different light radiation pattern as shown in FIGS. 6a–8b. LEDs with a high dome “lambertian” lens produce a “half globe” of light with a viewing angle of approximately 140 degrees (see FIGS. 7a, 7b). A majority of the light from a lambertian-lens LED is projected within an angle of approximately 30° relative to an optical axis of the lens (0° angular displacement). However, significant quantities of light are radiated at angles exceeding 50° relative to the LED lens optical axis (the above mentioned “half globe”).
LEDs are attractive to lighting designers in part because the light they produce is typically of a very narrow spectrum, e.g., of a single pure color, such as red, blue, green, amber, etc. In the prior art, to achieve a colored light output, white light was produced and typically filtered through a colored lens or other colored material, such as a colored glass bulb to produce the desired light color. This approach wasted a large percentage of the available light and consequently the electrical energy used to produce the light, reducing the energy efficiency of the prior art devices. The efficiency of LEDs as producers of colored light is enhanced because no external color filtering is needed.
U.S. Pat. No. 6,318,886 (the '886 patent), assigned to the assignee of the present invention, the entire contents of which are hereby incorporated by reference into this specification, describes a high-flux LED assembly in which an array of LEDs are provided with a reflector surrounding each LED. A conical reflecting surface collects and redirects off-axis (wide angle) light from the LED. The conical reflectors redirect such “wide angle” light out the face of the assembly, increasing the effective light contribution of each LED. The high-flux LED assembly also discloses connecting the conical reflectors with grooves to improve the wide-angle visibility desirable in a warning or signaling light application. By concentrating a number of high-output LEDs in a relatively small area and reflecting the light produced in a desired pattern, a very efficient and effective signaling and/or warning light is provided.
The '886 patent discloses an approach using conical reflectors. While the high-flux LED assembly described in the '886 patent has proved successful for its desired application, further improvements are possible. The conical reflectors disclosed in the '886 patent redirect light incident upon them out the face of the light assembly over a range of angles where the angle of the escaping light depends on the angular relationship between incident light and the reflecting surface. Such an arrangement, while desirably redirecting light out the front face of the assembly, undesirably does so over a range of angles. Some of the reflected light reinforces light output of the LED, while other light is reflected at random angles that fail to reinforce the light output of the LED and is effectively lost. The light pattern produced is essentially a series of bright points of light having somewhat improved wide-angle visibility due to the grooves connecting the conical reflectors.
It is known in the art to use parabolic reflectors to collimate the light output from prior art light sources such as halogen bulbs or xenon flash tubes. U.S. Pat. Nos. 4,792,717 and 4,886,329, both directed to a wide-angle warning light and both assigned to the assignee of the present invention, disclose the use of a parabolic reflector comprised of a linear parabolic section including parabolic dish ends. The reflecting surface has a linear focal axis similar in configuration to the reflecting surface associated with the xenon flash tube light source.
As exemplified by the '886, '717 and '329 patents discussed above, reflectors for light assemblies are typically configured to complement the form of the light source, e.g., point light sources are provided with reflectors having axial symmetry and linear light sources are provided with reflectors having linear symmetry. The conventional approach generally involved matching the reflector to the light source to produce maximum light output from a light assembly.